Display with an electrically conducting layer

ABSTRACT

A display for showing text and graphical images includes an electrically conducting layer which is connected to a shield potential, such as a ground potential, for shielding the display from external electromagnetic disturbances and preventing radiation from the display of electromagnetic disturbances generated by the display.

[0001] The invention relates to a display with an electrically conducting layer. Displays with an electrically conducting layer are known in the prior art and are used to make the display form a so-called “touch screen” or, for example in the case of liquid-crystal displays, to heat them. Heating devices are used in the case of liquid-crystal displays in order that they can operate quickly even at low temperatures, as may occur for example when they are used in motor vehicles, and in this way prevent a display with a slow response.

[0002] A “touch screen” is known in the prior art and is used to allow menus, submenus, values or icons represented on a screen to be selected by touching the respective representation with a finger or some other input means. In the case of an analog resistive touch screen, a plate of toughened glass with an electrically conductive coating with a uniform electrical resistance is arranged in front of the display. A sheet of polyester is stretched over this glass upper side and separated from it by small, transparent insulating points. The variable sheet has a hard, durable coating on the outer side and a conductive and highly transparent indium-tin-oxide coating on the inside. Even when touched lightly, the conductive coating establishes an electrical connection with the coating on the glass. By means of an integrated controller, a voltage gradient is set up on the conductive coating. The voltages at the contact point form an image of the touched position with the aid of analog values. The controller digitizes these voltages and sends them to a processing device to determine the touched positions.

[0003] A capacitive touch screen comprises a clear plate which has been coated with a resistively capacitive material and an insulating material. An electromagnetic field is generated over the plate. If a conducting object, for example a finger or metal rod, touches the screen and grounds it, the electromagnetic field changes. The place which was touched can be concluded from the change in the electromagnetic field.

[0004] Displays and the driver circuits controlling them are operated with high frequencies. Consequently, undesired electromagnetic disturbances can occur in the area surrounding the displays. If a display is used in an instrument cluster of a motor vehicle, the radio reception and/or the cell phone reception in the motor vehicle for example may be disturbed.

[0005] It is therefore the object of the invention to provide a display with an electrically conducting layer which causes the least possible electromagnetic disturbances and does not allow electromagnetic disturbances caused by the drive electronics to pass through and which is constructed in a simple and inexpensive way. This object is achieved according to the invention by the electrically conducting layer being connected to a shielding potential for high frequencies. The effect of this is that the electrically conducting layer is at the shielding potential for high frequencies and high frequencies are consequently prevented from passing through. The high-frequency connection may take place for example with capacitors which are arranged between the electrically conducting layer and the shielding potential, one terminal of the capacitor being connected to the electrically conducting layer and one terminal being connected to the shielding potential. In cases in which a DC connection between the electrically conducting layer and the shielding potential is unproblematical, it is also possible to establish the connection of the heating and the shielding potential by an electrically conductive element.

[0006] The shielding potential may be realized for example by a metal housing or by a metallized housing, the housing being closed by the display. Under some circumstances, depending on the required shielding effect, it may be adequate to connect the liquid-crystal display to a ground potential by a high-frequency connection.

[0007] The electrically conducting layer may be made up of indium-tin oxide (ITO), which covers the display over its surface area.

[0008] If the display is formed as a liquid-crystal display, the electrically conducting layer may be formed as a heating device, which is flowed through by a heating current. It is also possible to realize the heating device by means of current-conducting paths, which are arranged individually or in a meandering form. If these paths run between the electrodes of the liquid-crystal cells and consist of indium-tin oxide, they can be produced in one operation with the electrodes of the liquid-crystal cells.

[0009] It is also possible for the electrically conducting layer to be formed as part of a touch screen. In this case, the display may be formed for example as a liquid-crystal display, OLED display or as a monitor. If the display is formed as a liquid-crystal display, and an electrically conducting layer of a touch screen is arranged in front of it, the electrically conducting layer may also be used at the same time as heating for the liquid-crystal display.

[0010] The invention is explained in more detail below on the basis of the figures, in which:

[0011]FIG. 1 shows a partial section of a liquid-crystal cell with heating applied over its surface area and the connection to a shielding potential;

[0012]FIG. 2 shows the exploded drawing of a front and rear wall of a liquid-crystal cell;

[0013]FIG. 3 shows the section through a liquid-crystal cell and a shielding housing;

[0014]FIG. 4 shows a touch screen with a monitor in an exploded representation.

[0015] In FIG. 1, a liquid-crystal cell 1 has a front wall 2 a and a rear wall 2 b. On the front wall 2 a and the rear wall 2 b, heating layers 3 a, 3 b have been respectively applied over their surface area and are respectively separated from front and rear electrodes 5 a, 5 b by insulations 4 a, 4 b. The front and rear electrodes 5 a, 5 b are finally separated from a liquid-crystal substance 7 by insulations 6 a, 6 b. The front and rear heating layers 3 a, 3 b are connected to a ground potential M via contact clips 8 a, 8 b, electrical conductors 9 a, 9 b, capacitors 10 a, 10 b. Consequently, high-frequency disturbances impinging on the heating layers 3 a, 3 b can be conducted via the contact clips 8 a, 8 b electrical conductors 9 a, 9 b capacitors 10 a, 10 b to the ground potential M.

[0016] An adhesive bond 11 connects the front wall 2 a to the rear wall 2 b and prevents any escape of the liquid-crystal substance 7.

[0017] The driving of the electrodes 5 a, 5 b for influencing the liquid-crystal substance 7 has long been known and is therefore not explained any further here.

[0018] In FIG. 2, a front wall 12 a and a rear wall 12 b of another liquid-crystal cell can be seen. Arranged on the front wall 12 a are electrodes 13 a and arranged on the rear wall 12 b are electrodes 13 b. Arranged between the electrodes 13 a of the front wall 12 a are heating wires 14 a, which are connected to one another via contact pins 15 and connections 16 a arranged on the rear wall 12 b and are consequently connected in series. Arranged between the electrodes 13 b of the rear wall are heating wires 14 b, which are likewise connected via contact pins (not represented) and connections 16 b arranged on the front wall 12 a and are consequently connected in series. The heating wires 14 a, 14 b are connected via terminals 17 a, 17 b to a shielding potential (not represented). The arrangement of the heating wires 16 a, 16 b at right angles in relation to one another produces an arrangement of the heating wires 16 a, 16 b in the overall form of a grid, so that, with a high-frequency connection to a shielding potential, [lacuna] prevent high frequencies from passing through a display which has the components represented in FIG. 2.

[0019]FIG. 3 shows a liquid-crystal cell 1 with a heating (not represented), which may be configured in the same way as the heatings of the liquid-crystal cells represented in FIG. 1 or 2. The heating device is electrically connected to a shielding housing 20 via contact clips 8 a, 8 b and capacitors 10 a, 10 b. The shielding housing 10 may be produced from metal or be coated with a metal. Consequently, the interior of the shielding housing 20 is largely isolated for high frequencies from the area surrounding the shielding housing. No disturbances can penetrate into the interior from outside. Similarly, disturbances which are caused by a driving circuit 21 also cannot get through to the outside and consequently disturb devices in the area surrounding the liquid-crystal cell 1.

[0020] In FIG. 4, a monitor 21, a glass layer. 22, transparent metal films 23, 24, an electron raster 25 and a glass layer 26 can be seen. The metal films 23, 24 have been vapor-deposited on the glass layer 22. The electron raster 25 has been vapor-deposited in the edge region on the metal film 23. The glass layer 26 has been applied to protect the touch screen. A low AC voltage is applied to the electron raster 25 at all four corners.

[0021] If the surface of the screen is then touched by a finger, the potential of the finger draws a tiny amount of charge from each corner point. Since the current flow from four corners of the touch screen is proportional to the distance between the corner and the point touched, the precise location at which the touch screen was touched can be calculated and consequently the menu, submenu represented [lacuna] this region of the monitor, or the displayed value or icon can be selected. The metal film 24 is connected to the ground potential M via a capacitor 10. Consequently, high-frequency electromagnetic radiations of the monitor or of some other display present in place of the monitor 21 are shielded.

[0022] If a liquid-crystal display is used in place of the monitor 21, the metal film 24 may be used at the same time for heating the liquid-crystal display. 

1. A display (1) with an electrical layer (3 a, 3 b, 14 a, 14 b), characterized in that the electrically conducting layer (3 a, 3 b, 14 a, 14 b) is connected to a shielding potential (M, 20) for high frequencies.
 2. The display as claimed in claim 1, characterized in that the electrically conducting layer (3 a, 3 b, 14 a, 14 b) is connected to a shielding potential (M, 20) via capacitances.
 3. The display as claimed in claim 2, characterized in that the capacitances are realized as capacitors (10 a, 10 b).
 4. The display as claimed in one of the preceding claims, characterized in that the shielding potential is realized as a metal housing (20) or metallized housing which is closed by the display (1).
 5. The display as claimed in one of the preceding claims, characterized in that a ground potential (M) is used the as shielding potential.
 6. The display as claimed in one of the preceding claims, characterized in that the electrically conducting layer (3 a, 3 b) is made up of indium-tin oxide and covers the liquid-crystal display (1) over its surface area.
 7. The display as claimed in one of the preceding claims, characterized in that the display is formed as a liquid-crystal display, in that the electrically conducting layer (3 a, 3 b, 14 a, 14 b) is formed as a heating device.
 8. The display as claimed in one of claims 1-5, characterized in that the electrically conducting layer is configured as a heating device and comprises current-conducting paths (14 a, 14 b), which are arranged on the liquid-crystal display.
 9. The display as claimed in claim 7, characterized in that the current-conducting paths (14 a, 14 b) are arranged between electrodes (13 a, 13 b) of the liquid-crystal display.
 10. The display as claimed in claim 7 or 8, characterized in that the current-conducting paths (14 a, 14 b) are produced from indium-titanium oxide.
 11. The display as claimed in one of claims 1 to 6, characterized in that the electrically conducting layer is formed as part of a touch screen.
 12. The display as claimed in claim 11, characterized in that the display is formed as a liquid-crystal display, in that the electrically conducting layer is also used for heating the liquid-crystal display. 